Image forming method, image forming apparatus, and method for manufacturing printed matter

ABSTRACT

An image forming method is provided. The method includes the steps of (a) applying an ink to a recording medium to form an image and (b) applying a pressure to the recording medium to which the ink has been applied. The ink comprises water, an organic solvent, and a colorant. When the ink is formed into an ink film, a maximum value of logarithmic damping ratio of the ink film is 1.50 or less and a time elapsed until the logarithmic damping ratio reaches the maximum value is 3,800 seconds or less, when measured by a rigid-body pendulum test at 60° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2016-218335 and2017-195149, filed on Nov. 8, 2016 and Oct. 5, 2017, respectively, inthe Japan Patent Office, the entire disclosure of each of which ishereby incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to an image forming method, an imageforming apparatus, and a method for manufacturing printed matter.

Description of the Related Art

Inkjet recording devices have advantages that noise is low andoperability is high. In addition, inkjet recording devices are easy toproduce color images on plain paper. For this reason, inkjet recordingdevices are now widely diffusing from home use to office use.

Inkjet technology has also been applied to digital printers forindustrial use. For example, printers capable of recording informationwith solvent ink or ultraviolet-curable ink on non-absorptive recordingmedia have been put into a market. On the other hand, demand forwater-based inks is increasing for environmental protection.

Conventional water-based inkjet inks have been developed for limitedapplications, e.g., for plain paper or special paper such as glossyphoto paper. On the other hand, there is an increasing demand forextended application of inkjet printing for coated paper. However, sincecoated paper is poor in permeability, it is generally difficult tostrongly fix pigments on coated paper, resulting in an image with poorabrasion resistance.

SUMMARY

In accordance with some embodiments of the present invention, an imageforming method is provided. The method includes the steps of (a)applying an ink to a recording medium to form an image and (b) applyinga pressure to the recording medium to which the ink has been applied.The ink comprises water, an organic solvent, and a colorant. When theink is formed into an ink film, a maximum value of logarithmic dampingratio of the ink film is 1.50 or less and a time elapsed until thelogarithmic damping ratio reaches the maximum value is 3,800 seconds orless, when measured by a rigid-body pendulum test at 60° C.

In accordance with some embodiments of the present invention, an imageforming apparatus is provided. The image forming apparatus includes afirst ink applier, a pressurizer, and an ink. The first ink applier isconfigured to apply an ink to a recording medium to form an image. Thepressurizer is configured to apply a pressure to the recording medium towhich the ink has been applied. The ink comprises water, an organicsolvent, and a colorant. When the ink is formed into an ink film, amaximum value of logarithmic damping ratio of the ink film is 1.50 orless and a time elapsed until the logarithmic damping ratio reaches themaximum value is 3,800 seconds or less, when measured by a rigid-bodypendulum test at 60° C.

In accordance with some embodiments of the present invention, a methodof manufacturing printed matter is provided. The method includes thesteps of (a) applying an ink to a recording medium to form an image and(b) applying a pressure to the recording medium to which the ink hasbeen applied. The ink comprises water, an organic solvent, and acolorant. When the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an image forming apparatus in accordancewith some embodiments of the present invention that uses a continuoussheet;

FIG. 2 is a graph showing a relation between logarithmic damping ratioand elapsed time;

FIG. 3 is a schematic view of an image forming apparatus in accordancewith some embodiments of the present invention that is an inkjetrecording apparatus;

FIG. 4 is a magnified view of a recording head included in the imageforming apparatus illustrated in FIG. 3;

FIG. 5 is a perspective view of a continuous sheet (rolled sheet); and

FIG. 6 is a side view of the continuous sheet (rolled sheet) illustratedin FIG. 5.

The accompanying drawings are intended to depict example embodiments ofthe present invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes” and/or “including”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Embodiments of the present invention are described in detail below withreference to accompanying drawings. In describing embodimentsillustrated in the drawings, specific terminology is employed for thesake of clarity. However, the disclosure of this patent specification isnot intended to be limited to the specific terminology so selected, andit is to be understood that each specific element includes all technicalequivalents that have a similar function, operate in a similar manner,and achieve a similar result.

For the sake of simplicity, the same reference number will be given toidentical constituent elements such as parts and materials having thesame functions and redundant descriptions thereof omitted unlessotherwise stated.

In accordance with some embodiments of the present invention, an imageforming method is provided that is capable of forming an image thatcauses no offset even under pressure, while exhibiting high blockingresistance, excellent abrasion resistance, and high gloss.

Image Forming Method, Image Forming Apparatus, and Image Forming System

In accordance with some embodiments of the present invention, an imageforming method is provided that includes the steps of: (a) applying anink to a recording medium to form an image (hereinafter “first inkapplying process”); and (b) applying a pressure to the recording mediumto which the ink has been applied (hereinafter “pressurizing process”).The ink comprises water, an organic solvent, and a colorant. When theink is formed into an ink film, a maximum value of logarithmic dampingratio of the ink film is 1.50 or less and a time elapsed until thelogarithmic damping ratio reaches the maximum value is 3,800 seconds orless, when measured by a rigid-body pendulum test at 60° C. The pressuremay be in the range of from 3.5 to 8.0 kg/cm². The image forming methodmay further include other processes.

This image forming method is achieved based on the finding that imagesformed with conventional rolled sheet conveyers are poor in blockingresistance.

In addition, the inventors of the present invention have found thefollowing fact.

Adding a resin emulsion to an ink is known to be one technique forimproving fixability of the ink. However, such a resin capable ofimproving fixability generally exhibits high elasticity and thus themaximum value of logarithmic damping ratio of the ink is raised byaddition of the resin. The inventors of the present invention have foundthat as the maximum value of logarithmic damping ratio gets larger, theimage gets transferred (or offset) from the recording medium at the timea pressure is applied to the image, such as a time of fixing the imageon the recording medium by a fixing roller, or winding the recordingmedium in a case in which the recording medium is a rolled sheet.

FIG. 1 illustrates an image forming apparatus that uses a continuoussheet. This image forming apparatus includes a sheet feeder 1, arecording medium 2, a pretreatment liquid applier 3, an ink dischargehead 4, and a dryer 5. In this image forming apparatus, when thecontinuous sheet is wound in a roll after an image is formed thereon, alarge pressure is applied to around the central part of the roll tocause offset of the image.

Offset of the image can be caused not only at around the central partbut also at the peripheral part of the roll when, for example, thecontinuous sheet is rewound by tension and a large pressure is appliedthereto. There is a case in which a second ink applying process(hereinafter may be referred to as “additional printing”) is furtherperformed after the continuous sheet is wound up after the first inkapplying process. In the second ink applying process, an ink is furtherapplied to the same side of the continuous sheet to which the ink hasbeen already applied in the first ink applying process. In this case, ifthe winding pressure after the first ink applying process is large, thecontinuous sheet will be wound in a uniform roll and a clear image willbe formed thereon in the second ink applying process. However, therestill remains the problem of image offset. On the other hand, if thewinding pressure is small, the continuous sheet will be wound in anonuniform roll that is not stretched but retain slack. As a result, inthe second ink applying process, the sheet cannot be fed at a constantspeed and a position misalignment may occur.

In accordance with some embodiments of the present invention, the ink ispreferably applied to the same side of the recording medium in both thefirst and second ink applying processes, because the above problem hasbeen solved. Of course, the ink may be applied to the opposite sides ofthe recording medium in the first and second ink applying processes,respectively.

In accordance with some embodiments of the present invention, an imageforming apparatus is provided that includes: a first ink applierconfigured to apply an ink to a recording medium to form an image; apressurizer configured to apply a pressure to the recording medium towhich the ink has been applied; and an ink comprising water, an organicsolvent, and a colorant. When the ink is formed into an ink film, amaximum value of logarithmic damping ratio of the ink film is 1.50 orless and a time elapsed until the logarithmic damping ratio reaches themaximum value is 3,800 seconds or less, when measured by a rigid-bodypendulum test at 60° C. The pressure may be in the range of from 3.5 to8.0 kg/cm².

In accordance with some embodiments of the present invention, an imageforming system is provided that includes: a first ink applier configuredto apply an ink to a recording medium to form an image; a pressurizerconfigured to apply a pressure to the recording medium to which the inkhas been applied; and an ink comprising water, an organic solvent, and acolorant. When the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C. The pressure may be in the range of from 3.5 to 8.0 kg/cm².

Logarithmic Damping Ratio

When the ink is formed into an ink film, the maximum value oflogarithmic damping ratio of the ink film is 1.50 or less, preferablyfrom 0.01 to 1.50, and more preferably from 0.7 to 1.50, when measuredby a rigid-body pendulum test at 60° C. When the maximum value oflogarithmic damping ratio is 1.50 or less, the ink film is suppressedfrom becoming sticky and thus the occurrence of blocking is prevented.

The time elapsed until the logarithmic damping ratio reaches the maximumvalue is 3,800 seconds or less, preferably from 100 to 3,800 seconds,and more preferably 1,700 to 3,800 seconds. When the time elapsed untilthe logarithmic damping ratio reaches the maximum value is 3,800 secondsor less, the ink film forming speed can be increased and the occurrenceof blocking can be prevented. Here, the time elapsed until thelogarithmic damping ratio reaches the maximum value is measured from thetime of starting measurement of logarithmic damping ratio.

When the maximum value of logarithmic damping ratio is 1.50 or less andthe time elapsed until the logarithmic damping ratio reaches the maximumvalue is 3,800 seconds or less, the image causes no blocking even when apressure of from 3.5 to 8.0 kg/m² is applied thereto while exhibitinghigh abrasion resistance and gloss. In addition, as tackiness of the inkfilm is less likely to increase during the ink film formation process,the ink film is prevented from sticking to the backing sheet and thusthe occurrence of blocking is suppressed. Because no blocking willoccur, it is possible to wind the sheet tightly, thus improvingfixability. As the sheet is wound tightly, the surface of the image issmoothened and glossiness is increased.

The logarithmic damping ratio is determined as follows.

As a measuring instrument, a Rigid-body Pendulum Type PhysicalProperties Testing Instrument RPT-3000W (available from A&D Company,Limited) is used. An ink film is formed by dropping 40 μL of the inkonto an aluminum substrate and spreading the dropped ink into a filmhaving a thickness of 100 μm using a coating jig (PCT-100). The ink filmis immediately set along with a cold block (CHB-100). A cylinder edge(RBP-040) and a pendulum (FRB-100) are set up, and two weights exclusivefor FRB-100 are set at the lowest part of the pendulum. The measurementtemperature is raised from normal temperature (25° C.) to 60° C. at arate of 5° C./min and kept at 60° C. thereafter. The logarithmic dampingratio and temperature are plotted along the time. The obtained curve issmoothened and the maximum value thereof is calculated to determine themaximum value of logarithmic damping ratio. The maximum value oflogarithmic damping ratio can indicate a force related to tackiness.

A logarithmic damping ratio (D′(n)) after the smoothing can bedetermined from the following formulae, where D(n) representslogarithmic damping ratio of the n^(th) plot.D′(n)={D(n−2)+D(n−1)+D(n)+D(n+1)+D(n+2)}/5D′(1)=D(1)D′(2)={D(1)+D(2)}/2

FIG. 2 is a graph showing a relation between logarithmic damping ratioand elapsed time. Referring to FIG. 2, with respect to Sample A, themaximum value of logarithmic damping ratio is in excess of 1.50 and thetime elapsed until the logarithmic damping ratio reaches the maximumvalue is in excess of 3,800 seconds. By contrast, with respect to SampleB, the maximum value of logarithmic damping ratio is 1.50 or less andthe time elapsed until the logarithmic damping ratio reaches the maximumvalue is 3,800 seconds or less. When the maximum value of logarithmicdamping ratio is 1.50 or less and the time elapsed until the logarithmicdamping ratio reaches the maximum value is 3,800 seconds or less, as isthe case with Sample B, blocking resistance, abrasion resistance, andglossiness are improved.

Pressure in Pressurizing Process

In the pressurizing process, the pressure applied to the recordingmedium to which the ink has been applied is in the range of from 3.5 to8.0 kg/cm², and preferably from 3.5 to 7.3 kg/cm². When the pressure is3.5 kg/cm² or more, the image can be sufficiently fixed and abrasionresistance of the image is improved. When the pressure is 8.0 kg/cm² orless, the image is prevented from being offset to a pressure roller,stacked image, or paper sheet. There is no limit on how to measure thepressure. The pressure can be measured by any known device. Even in acase in which the pressure is generated by winding the continuous sheetin a roll after the ink has been applied thereto, there is no limit onhow to measure the pressure. For example, an instrument I-SCAN 5027(available from Nitta Corporation) can be used to measure the pressure.

The pressure applied to the recording medium to which the ink has beenapplied is equivalent to the set pressure of the pressure roller.

It is possible to adjust the pressure within the range of from 3.5 to8.0 kg/cm² by simply stacking the pressure roller on the image withoutapplying tension.

In this case, for example, the pressure becomes 3.5 kg/m² and 8.0 kg/m²when the diameter (winding thickness) of the roll is 0.5 m and 1.5 m,respectively.

The pressure applied to the rolled continuous sheet may be calculatedfrom diameter, height, and mass of the rolled continuous sheet that canbe determined from photographs and information thereof.

In the pressurizing process, in a case in which the recording medium isa continuous sheet, it is preferable that the pressure is generated asthe continuous sheet to which the ink gas been applied is wound in aroll.

When the maximum value of logarithmic damping ratio and the time elapseduntil the logarithmic damping ratio reaches the maximum value are withinin the above-specified ranges, the image causes no offset when apressure within the above-specified range is applied thereto, whileexhibiting blocking resistance, abrasion resistance, and highglossiness. In addition, when the pressure is within the above-specifiedrange, the winding pressure is sufficient to perform the additionalprinting without any problem.

First Ink Applying Process and First Ink Applier

The first ink applying process is a process in which an ink is appliedto a recording medium to form an image.

The first ink applier is configured to apply an ink to a recordingmedium to form an image.

The first ink applying process is preferably performed by the first inkapplier.

The maximum value of logarithmic damping ratio of the ink film and thetime elapsed until the logarithmic damping ratio reaches the maximumvalue vary depending on the types of compositional materials (e.g.,resin) of the ink. Preferred types and amounts of resins to be added tothe ink, for achieving the preferred maximum value of logarithmicdamping ratio and the preferred time elapsed until the logarithmicdamping ratio reaches the maximum value, are described later.

Ink

Compositional materials of the ink (e.g., organic solvent, water,colorant, resin, and other additives) are described in detail below.

Organic Solvent

There is no specific limitation on the type of the organic solvent. Forexample, water-soluble organic solvents are usable. Examples ofwater-soluble organic solvents include polyols, ethers (e.g., polyolalkyl ethers, polyol aryl ethers), nitrogen-containing heterocycliccompounds, amides, amines, and sulfur-containing compounds.

Specific examples of the water-soluble organic solvents include, but arenot limited to, polyols such as ethylene glycol, diethylene glycol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethyleneglycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol,1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol,1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol,1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol,ethyl-1,2,4-butanetriol, 1,2,3-butanetriol,2,2,4-trimethyl-1,3-pentanediol, and 3-methyl-1,3,5-pentanetriol; polyolalkyl ethers such as ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycolmonomethyl ether, and propylene glycol monoethyl ether; polyol arylethers such as ethylene glycol monophenyl ether and ethylene glycolmonobenzyl ether; nitrogen-containing heterocyclic compounds such as2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone;amides such as formamide, N-methylformamide, N,N-dimethylformamide,3-methoxy-N,N-dimethyl propionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, andtriethylamine; sulfur-containing compounds such as dimethyl sulfoxide,sulfolane, and thiodiethanol; propylene carbonate; and ethylenecarbonate.

In particular, organic solvents having a boiling point of 250° C. orless are preferable since they can function as a wetting agent whileproviding good drying property.

In addition, polyol compounds having 8 or more carbon atoms and glycolether compounds are also preferable. Specific examples of the polyolcompounds having 8 or more carbon atoms include, but are not limited to,2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

Specific examples of the glycol ether compounds include, but are notlimited to, polyol alkyl ethers such as ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monobutyl ether,triethylene glycol monobutyl ether, tetraethylene glycol monomethylether, and propylene glycol monoethyl ether; and polyol aryl ethers suchas ethylene glycol monophenyl ether and ethylene glycol monobenzylether.

In particular, the polyol compounds having 8 or more carbon atoms andthe glycol ether compounds, exemplified above, are capable of improvingpaper-permeability of the ink, which is advantageous when the ink isprinted on a recording medium made of paper.

Preferably, the glycol ether compound has no hydroxyl group. Specificpreferred examples of the glycol ether compound having no hydroxy groupinclude the glycol ether compound represented by the following formula(1).

In the formula (1), R¹ represents a hydrogen atom or alkyl group having1 to 10 carbon atoms, each of R² and R³ independently represents analkyl group having 1 to 10 carbon atoms, and n represents an integer offrom 1 to 5.

In the formula (1), R¹ represents a hydrogen atom or alkyl group having1 to 10 carbon atoms, preferably a hydrogen atom or methyl group.

In the formula (1), R² represents an alkyl group having 1 to 10 carbonatoms, preferably methyl group or ethyl group.

In the formula (1), R³ represents an alkyl group having 1 to 10 carbonatoms, preferably methyl group, ethyl group, or butyl group.

In the formula (1), n represents an integer of from 1 to 5, preferablyfrom 2 to 3.

Specific examples of the glycol ether compound represented by theformula (1) include, but are not limited to, tripropylene glycolmonobutyl ether, triethylene glycol dimethyl ether, diethylene glycoldiethyl ether, dipropylene glycol dimethyl ether, and tripropyleneglycol dimethyl ether.

Preferably, the content rate of the organic solvent in the ink is in therange of from 10% to 60% by mass, more preferably from 20% to 60% bymass, and most preferably from 2.0% to 8.0% by mass, for drying propertyand discharge reliability of the ink.

Resin

The ink may comprise a resin. Specific examples the resin include, butare not limited to, urethane resin, polyester resin, acrylic resin,vinyl acetate resin, styrene resin, butadiene resin, styrene-butadieneresin, vinyl chloride resin, acrylic styrene resin, and acrylic siliconeresin.

These resins may be in the form of particles (hereinafter “resinparticles”). The resin particles may be dispersed in water to become aresin emulsion. The ink can be obtained by mixing the resin emulsionwith other materials such as colorant and organic solvent. The resinparticles are available either synthetically or commercially. The resinparticles may include one type or two or more types of resin particles.

For abrasion resistance, urethane resin particles are preferable.

Urethane Resin Particles

The urethane resin particles may comprise polyurethane that is obtainedby binding an isocyanate compound having multiple isocyanate groups witha polyol compound having multiple hydroxyl groups by urethane bonds.Each of the isocyanate compound and the polyol compound may be a polymercompound itself.

Isocyanate Compound

Examples of the isocyanate compound having multiple isocyanate groupsused to obtain polyurethane include, but are not limited to,difunctional isocyanate compounds, trifunctional isocyanate compounds,and tetrafunctional isocyanate compounds. Each of these compounds can beused alone or in combination with others.

Specific examples of the difunctional isocyanate compounds include, butare not limited to, isophorone diisocyanate, cyclohexane diisocyanate,1,6-hexane diisocyanate, 1,4-butane diisocyanate, 1,4-benzenediisocyanate, and diphenylmethane diisocyanate.

Specific examples of the trifunctional isocyanate compounds include, butare not limited to, 1,3,5-cyclohexane triisocyanate, 1,4,8-octanetriisocyanate, and 1,3,5-benzene triisocyanate.

Specific examples of the tetrafunctional isocyanate compounds include,but are not limited to, 1,2,5,6-cyclohexane tetraisocyanate.

The resulting polyurethane is varied in mechanical strength and faderesistance depending on the type of isocyanate compound used. Amongthese compounds, isophorone diisocyanate and cyclohexane diisocyanateare preferable in terms of handling property in mass production,environmental conservation, and operability of physical properties.

Polyol Compound

Specific examples of the polyol compound include, but are not limitedto: alkylene glycols (e.g., ethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol); alkylene etherglycols (e.g., diethylene glycol, triethylene glycol, dipropyleneglycol, polyethylene glycol, polypropylene glycol, polytetramethyleneglycol); alicyclic diols (e.g., 1,4-cyclohexanedimethanol, hydrogenatedbisphenol A); bisphenols (e.g., bisphenol A, bisphenol F, bisphenol S);alkylene oxide (e.g., ethylene oxide, propylene oxide, butylene oxide)adducts of the alicyclic diols; 4,4′-dihydroxybiphenyls (e.g.,3,3′-difluoro-4,4′-dihydroxybiphenyl); bis(hydroxyphenyl)alkanes (e.g.,bis(3-fluoro-4-hydroxyphenyl)methane,1-phenyl-1,1-bis(3-fluoro-4-hydroxyphenyl)ethane,2,2-bis(3-fluoro-4-hydroxyphenyl)propane,2,2-bis(3,5-difluoro-4-hydroxyphenyl)propane (also known astetrafluorobisphenol A),2,2-bis(3-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane);bis(4-hydroxyphenyl) ethers (e.g., bis(3-fluoro-4-hydroxyphenyl) ether);and alkylene oxide (e.g., ethylene oxide, propylene oxide, butyleneoxide) adducts of the bisphenols. Each of these compounds can be usedalone or in combination with others.

Specific examples of the polyol compound further include carbonate-basedpolyols, ester-based polyols, and ether-based polyols. Each of thesecompounds can be used alone or in combination with others. Each of thesepolyol compounds has at least two hydroxyl groups.

Preferably, the polyol compound has hydroxyl groups on both terminalsfrom a synthetic point of view.

Specific preferred examples of the carbonate-based polyols include acompound represented by the following formula (A).

Specific preferred examples of the ester-based polyols include acompound represented by the following formula (B).

Specific preferred examples of the ether-based polyols include acompound represented by the following formula (C).H

O—R

_(n)OH  Formula (C)

In each of the formulae (A) to (C), R may independently representhexamethylene group, cyclohexane group, phenylene group, tetramethylenegroup, cyclohexane dimethylene group, or cyclohexane monomethylenegroup, but is not limited thereto. In addition, n represents a numeralof from 1 to 20.

The volume average particle diameter of the resin particles is notparticularly limited and can be suitably selected to suit to aparticular application. Preferably, the volume average particle diameteris in the range of from 10 to 1,000 nm, more preferably from 10 to 200nm, and most preferably from 10 to 100 nm, to obtain good fixability andhigh image hardness.

The volume average particle diameter of the resin particles can bemeasured with a particle size distribution analyzer (NANOTRAC WAVE-UT151available from MicrotracBEL Corp.).

Preferably, the content rate of the resin in the ink is in the range offrom 1% to 30% by mass, more preferably from 5% to 20% by mass, forfixability and storage stability of the ink.

Preferably, solid contents in the ink have a maximum frequency particlediameter in the range of from 20 to 1,000 nm, more preferably from 20 to150 nm, based on the number of solid contents, for improving dischargestability and image quality (e.g., image density) of the ink. The solidcontents include the resin particles and pigment particles. The particlediameter of the solid contents can be measured with a particle sizedistribution analyzer (NANOTRAC WAVE-UT151 available from MicrotracBELCorp.).

Mass Ratio of Glycol Ether Compound to Urethane Resin Particles

The mass ratio of the glycol ether compound to the urethane resinparticles is preferably in the range of from 0.4 to 2.4, more preferablyfrom 0.4 to 1.8, and most preferably from 1.2 to 1.8. When the massratio is from 0.4 to 2.4, it is easy to adjust the maximum value oflogarithmic damping ratio and the time elapsed until the logarithmicdamping ratio reaches the maximum value to 1.50 or less and 3,800seconds or less, respectively.

Colorant

Examples of the colorant include, but are not limited to, pigments anddyes.

The pigments include both inorganic pigments and organic pigments. Twoor more of the colorants can be used alone or in combination withothers. Mixed crystals can also be used as the colorant.

Examples of the pigments include black pigments, yellow pigments,magenta pigments, white pigments, green pigments, orange pigments,glossy color pigments (e.g., gold pigments, silver pigments), andmetallic pigments.

Specific examples of the inorganic pigments include, but are not limitedto, titanium oxide, iron oxide, calcium carbonate, barium sulfate,aluminum hydroxide, barium yellow, cadmium red, chrome yellow, andcarbon black produced by a known method, such as a contact method, afurnace method, and a thermal method.

Specific examples of the organic pigments include, but are not limitedto, azo pigments, polycyclic pigments (e.g., phthalocyanine pigments,perylene pigments, perinone pigments, anthraquinone pigments,quinacridone pigments, dioxazine pigments, indigo pigments, thioindigopigments, isoindolinone pigments, quinophthalone pigments), dye chelates(e.g., basic dye chelate, acid dye chelate), nitro pigments, nitrosopigments, and aniline black. Among these pigments, those having goodaffinity for the solvent are preferable. In addition, resin hollowparticles and inorganic hollow particles can also be used.

Specific examples of the pigments usable for black-and-white printinginclude, but are not limited to: carbon blacks (i.e., C.I. Pigment Black7) such as furnace black, lamp black, acetylene black, and channelblack; metals such as copper, iron (i.e., C.I. Pigment Black 11), andtitanium oxide; and organic pigments such as aniline black (i.e., C.I.Pigment Black 1).

Specific examples of the pigments usable for color printing include, butare not limited to: C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34,35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100,101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, and213; C.I. Pigment Orange 5, 13, 16, 17, 36, 43, and 51; C.I. Pigment Red1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B(Ca)), 48:3,48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2,64:1, 81, 83, 88, 101 (red iron oxide), 104, 105, 106, 108 (cadmiumred), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168,170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213,219, 224, 254, and 264; C.I. Pigment Violet 1 (rhodamine lake), 3, 5:1,16, 19, 23, and 38; and C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, and36.

Examples of the dyes include acid dyes, direct dyes, reactive dyes, andbasic dyes. Two or more of these dyes can be used in combination.

Specific examples of the dyes include, but are not limited to, C.I. AcidYellow 17, 23, 42, 44, 79, and 142, C.I. Acid Red 52, 80, 82, 249, 254,and 289, C.I. Acid Black 1, 2, 24, and 94, C. I. Food Black 1 and 2,C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, and173, C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227, C.I. Direct Black19, 38, 51, 71, 154, 168, 171, and 195, C.I. Reactive Red 14, 32, 55,79, and 249, and C.I. Reactive Black 3, 4, and 35.

Preferably, the content rate of the colorant in the ink is in the rangeof from 0.1% to 15% by mass, more preferably from 1% to 10% by mass, forimproving image density, fixing strength, and discharge stability.

The pigment can be dispersed in the ink by any of the following methods:introducing a hydrophilic functional group to the pigment to make thepigment self-dispersible; covering the surface of the pigment with aresin; and dispersing the pigment by a dispersant.

In the method of introducing a hydrophilic functional group to thepigment to make the pigment self-dispersible, for example, a functionalgroup such as sulfone group and carboxyl group may be introduced to thepigment (e.g., carbon) to make the pigment dispersible in water.

In the method of covering the surface of the pigment with a resin, forexample, the pigment may be incorporated in a microcapsule to make thepigment self-dispersible in water. In this case, the pigment may bereferred to as a resin-covered pigment. In this case, not all thepigment particles included in the ink should be covered with a resin. Itis possible that a part of the pigment particles are not covered withany resin or partially covered with a resin.

In the method of dispersing the pigment by a dispersant, low-moleculardispersants and high-molecular dispersants, represented by knownsurfactants, may be used.

More specifically, any of anionic surfactants, cationic surfactants,ampholytic surfactants, and nonionic surfactants may be used as thedispersant depending on the property of the pigment.

For example, a nonionic surfactant RT-100 (product of Takemoto Oil & FatCo., Ltd.) and sodium naphthalenesulfonate formalin condensate arepreferably used as the dispersant.

One dispersant can be used alone, and two or more dispersants can beused in combination.

Pigment Dispersion

The ink can be obtained by mixing the pigment with other materials suchas water and the organic solvent. The ink can also be obtained by,first, preparing a pigment dispersion by mixing the pigment with water,a pigment dispersant, etc., and thereafter mixing the pigment dispersionwith other materials such as water and the organic solvent.

The pigment dispersion can be obtained by mixing water, the pigment, apigment dispersant, and other components, if any. The pigment isdispersed in the pigment dispersion with the adjusted particle diameter.Preferably, the pigment dispersion is prepared with a disperser.

Preferably, the pigment dispersed in the pigment dispersion has amaximum frequency particle diameter in the range of from 20 to 500 nm,more preferably from 20 to 150 nm, based on the number of pigmentparticles, for improving dispersion stability of the pigment anddischarge stability and image quality (e.g., image density) of the ink.The particle diameter of the pigment can be measured with a particlesize distribution analyzer (NANOTRAC WAVE-UT151 available fromMicrotracBEL Corp.).

Preferably, the content rate of the pigment in the pigment dispersion isin the range of from 0.1% to 50% by mass, more preferably from 0.1% to30% by mass, for improving discharge stability and image density.

Preferably, the pigment dispersion may be subjected to filtration usinga filter or a centrifugal separator to remove coarse particles, andthereafter to degassing.

Water

Preferably, the content rate of water in the ink is in the range of from10% to 90% by mass, more preferably from 20% to 60% by mass, for dryingproperty and discharge reliability of the ink.

The water may be pure water such as ion-exchange water, ultrafiltrationwater, reverse osmosis water, and distilled water, or ultrapure water.Each of these waters can be used alone or in combination with others.

Additives

The ink may further contain a surfactant, a defoamer, a preservative, afungicide, a corrosion inhibitor, and/or a pH adjuster, if necessary.

Surfactant

Usable surfactants include silicone-based surfactants, fluorine-basedsurfactants, ampholytic surfactants, nonionic surfactants, and anionicsurfactants.

The silicone-based surfactants have no specific limit and can besuitably selected to suit to a particular application. Preferred aresilicone-based surfactants which are not decomposed even in a high pHenvironment. Specific examples thereof include, but are not limited to,side-chain-modified polydimethylsiloxane, both-end-modifiedpolydimethylsiloxane, one-end-modified polydimethylsiloxane, andside-chain-both-end-modified polydimethylsiloxane. In particular, thosehaving a polyoxyethylene group and/or a polyoxyethylene polyoxypropylenegroup as the modifying group are preferable because they demonstrategood characteristics as an aqueous surfactant. Specific examples of thesilicone-based surfactants further include polyether-modifiedsilicone-based surfactants, such as a dimethyl siloxane compound havinga polyalkylene oxide structure unit on a side chain thereof which isbonded to Si.

Specific preferred examples of the fluorine-based surfactants include,but are not limited to, perfluoroalkyl sulfonic acid compounds,perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphatecompounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkyleneether polymer compounds having a perfluoroalkyl ether group on its sidechain. These compounds have weak foaming property, which is preferable.Specific examples of the perfluoroalkyl sulfonic acid compounds include,but are not limited to, perfluoroalkyl sulfonic acid and perfluoroalkylsulfonate. Specific examples of the perfluoroalkyl carboxylic acidcompounds include, but are not limited to, perfluoroalkyl carboxylicacid and perfluoroalkyl carboxylate. Specific examples of thepolyoxyalkylene ether polymer compounds having a perfluoroalkyl ethergroup on a side chain include, but are not limited to, a sulfate of apolyoxyalkylene ether polymer having a perfluoroalkyl ether group on itsside chain, and a salt of a polyoxyalkylene ether polymer having aperfluoroalkyl ether group on its side chain. Specific examples of thecounter ions for these fluorine-based surfactants include, but are notlimited to, Li, Na, K, NH₄, NH₃CH₂CH₂OH, NH₂(CH₂CH₂OH)₂, andNH(CH₂CH₂OH)₃.

Specific examples of the ampholytic surfactants include, but are notlimited to, laurylaminopropionate, lauryl dimethyl betaine, stearyldimethyl betaine, and lauryl hydroxyethyl betaine.

Specific examples of the nonionic surfactants include, but are notlimited to, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylesters, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides,polyoxyethylene propylene block copolymers, sorbitan fatty acid esters,polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adductsof acetylene alcohol.

Specific examples of the anionic surfactants include, but are notlimited to, acetate, dodecylbenzene sulfonate, and laurate ofpolyoxyethylene alkyl ether, and polyoxyethylene alkyl ether sulfate.

Each of these compounds can be used alone or in combination with others.

Specific examples of the silicone-based surfactants include, but are notlimited to, side-chain-modified polydimethylsiloxane, both-end-modifiedpolydimethylsiloxane, one-end-modified polydimethylsiloxane, andside-chain-and-both-end-modified polydimethylsiloxane. Morespecifically, polyether-modified silicone-based surfactants havingpolyoxyethylene group and/or polyoxyethylene polyoxypropylene group asthe modifying groups are preferable since they exhibit good propertiesas an aqueous surfactant.

These surfactants are available either synthetically or commercially.Commercial products are readily available from BYK Japan KK, Shin-EtsuChemical Co., Ltd., Dow Corning Toray Co., Ltd., Nihon Emulsion Co.,Ltd., and Kyocisha Chemical Co., Ltd.

Specific examples of the polyether-modified silicone-based surfactantsinclude, but are not limited to, a compound represented by the followingformula (S-1) that is a dimethylpolysiloxane having a polyalkylene oxidestructure on its side chain bonded to Si atom.

In the formula (S-1), each of m, n, a, and b independently represents aninteger, R represents an alkylene group, and R′ represents an alkylgroup

Specific examples of commercially-available polyether-modifiedsilicone-based surfactants include, but are not limited to: KF-618,KF-642, and KF-643 (available from Shin-Etsu Chemical Co., Ltd.);EMALEX-SS-5602 and SS-1906EX (available from Nihon Emulsion Co., Ltd.);FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, and FZ-2164(available from Dow Corning Toray Co., Ltd); BYK-33 and BYK-387(available from BYK Japan KK); and TSF4440, TSF4452, and TSF4453(available from Momentive Performance Materials Inc.).

Preferably, the fluorine-based surfactant is a compound having 2 to 16fluorine-substituted carbon atoms, more preferably a compound having 4to 16 fluorine-substituted carbon atoms.

Specific examples of the fluorine-based surfactants include, but are notlimited to, perfluoroalkyl phosphate compounds, perfluoroalkyl ethyleneoxide adducts, and polyoxyalkylene ether polymer compounds having aperfluoroalkyl ether group on its side chain. Among these fluorine-basedsurfactants, polyoxyalkylene ether polymer compounds having aperfluoroalkyl ether group on its side chain are preferable sincefoaming property thereof is small. More specifically, compoundsrepresented by the following formula (F-1) and (F-2) are preferable.CF₃CF₂(CF₂CF₂)_(m)—CH₂CH₂O(CH₂CH₂O)_(n)H  Formula (F-1)

In the formula (F-1), m is preferably an integer ranging from 0 to 10,and n is preferably an integer ranging from 0 to 40, to givewater-solubility to the compound.C_(n)F_(2n+1)—CH₂CH(OH)CH₂—O—(CH₂CH₂O)_(a)—Y  Formula (F-2)

In the formula (F-2), Y represents H, C_(n)F_(2n+1) (where n representsan integer of from 1 to 6), CH₂CH(OH)CH₂—C_(n)F_(2n+1) (where nrepresents an integer of from 4 to 6), or C_(p)F_(2p+1) (where prepresents an integer of from 1 to 19); and a represents an integer offrom 4 to 14.

The fluorine-based surfactants are available either synthetically orcommercially.

Specific examples of commercially-available fluorine-based surfactantsinclude, but are not limited to: SURFLON S-111, S-112, S-113, S-121,S-131, S-132, S-141, and S-145 (available from Asahi Glass Co., Ltd.);Fluorad™ FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, andFC-431 (available from Sumitomo 3M Limited); MEGAFACE F-470, F-1405, andF-474 (available from DIC Corporation); Zonyl® TBS, FSP, FSA, FSN-100,FSN, FSO-100, FSO, FS-300, UR, CAPSTONE FS-30, FS-31, FS-3100, FS-34,and FS-35 (available from The Chemours Company); FT-110, FT-250, FT-251,FT-400S, FT-150, and FT-400SW (available from NEOS COMPANY LIMITED);PolyFox PF-136A, PF-156A, PF-151N, PF-154, and PF-159 (available fromOMNOVA Solutions Inc.); and UNIDYNE™ DSN-403N (available from DaikinIndustries, Ltd.). Among these, for improving printing quality, inparticular color developing property, paper permeability, paperwettability, and uniform dying property, FS-3100, FS-34, and FS-300(available from The Chemours Company), FT-110, FT-250, FT-251, FT-400S,FT-150, and FT-400SW (available from NEOS COMPANY LIMITED), PolyFoxPF-151N (available from OMNOVA Solutions Inc.), and UNIDYNE™ DSN-403N(available from Daikin Industries, Ltd.) are particularly preferred.

Preferably, the content rate of the surfactant in the ink is in therange of from 0.001% to 5% by mass, more preferably from 0.05% to 5% bymass, for improving wettability, discharge stability, and image quality.

Defoamer

Specific examples of the defoamer include, but are not limited to,silicone defoamers, polyether defoamers, and fatty acid ester defoamers.Two or more of these defoamers can be used alone or in combination withothers. Among these defoamers, silicone defoamers are preferable sincethey have excellent defoaming ability.

Preservative and Fungicide

Specific examples of the preservative and fungicide include, but are notlimited to, 1,2-benzisothiazoline-3-one.

Corrosion Inhibitor

Specific examples of the corrosion inhibitor include, but are notlimited to, acid sulphite and sodium thiosulfate.

pH Adjuster

The pH adjuster has no particular limit so long as it is capable ofadjusting the pH to 7 or higher. Specific examples of such a pH adjusterinclude, but are not limited to, amines such as diethanolamine andtriethanolamine.

The properties of the ink, such as viscosity, surface tension, and pH,are not particularly limited and can be suitably selected to suit to aparticular application.

Preferably, the ink has a viscosity at 25° C. in the range of from 5 to30 mPa·s, more preferably from 5 to 25 mPa·s, for improving printdensity and text quality and obtaining good dischargeability. Theviscosity can be measured at 25° C. by a rotatory viscometer (RE-80Lavailable from Toki Sangyo Co., Ltd.) equipped with a standard conerotor (1° 34′×R24), while setting the sample liquid amount to 1.2 mL,the number of rotations to 50 rotations per minute (rpm), and themeasuring time to 3 minutes.

Preferably, the ink has a surface tension of 35 mN/m or less, morepreferably 32 mN/m or less, at 25° C., so that the ink is suitablylevelized on a recording medium and the drying time of the ink isshortened.

Preferably, the ink has a pH in the range of from 7 to 12, morepreferably from 8 to 11, for preventing corrosion of metal materialscontacting the ink.

Recording Medium

Specific examples of the recording medium include, but are not limitedto, plain paper, glossy paper, special paper, clothes, film, overheadprojector (OHP) transparency, and general-purpose printing paper.

In particular, the recording medium preferably comprises a substrate anda coating layer disposed on at least one surface of the substrate, andoptionally includes other layers, if needed.

Such a recording medium comprising a substrate and a coating layer isgenerally called coated paper and known to have low ink permeability. Itis generally difficult to strongly fix a colorant on such a recordingmedium having low permeability, such as coated paper, and thus theresulting image becomes poor in abrasion resistance. On the other hand,when the maximum value of logarithmic damping ratio of the ink film is1.50 or less and the time elapsed until the logarithmic damping ratioreaches the maximum value is 3,800 seconds or less, when measured by arigid-body pendulum test at 60° C., the image causes no blocking evenwhen a pressure of from 3.5 to 8.0 kg/m² is applied thereto whileexhibiting high glossiness.

In a case in which the recording medium comprises a substrate and acoating layer, preferably, the transfer amount of pure water to therecording medium within a contact time of 100 ms is from 2 to 35 mL/m²,more preferably from 2 to 10 mL/m², when measured by a dynamic scanningabsorptometer.

When the transfer amount of pure water within a contact time of 100 msis too small, beading (i.e., a phenomenon in which adjacent dots attracteach other to make the image surface rough) may easily occur. When thetransfer amount of pure water within a contact time of 100 ms is toolarge, the ink dot diameter in the image becomes too smaller than adesired diameter.

In addition, preferably, the transfer amount of pure water to therecording medium within a contact time of 400 ms is from 3 to 40 mL/m²,more preferably from 3 to 10 mL/m², when measured by a dynamic scanningabsorptometer.

When the transfer amount of pure water within a contact time of 400 msis too small, drying property of the image is so poor that spur rollermark is easily made. When the transfer amount of pure water within acontact time of 400 ms is too large, glossiness of the dried imagebecomes too low. The transfer amount of pure water within a contact timeof 100 ms or 400 ms is measured at the surface of the recording mediumwhich has a coating layer thereon.

The dynamic scanning absorptometer (“DSA”) is an instrument capable ofaccurately measuring the amount of liquid absorption within an extremelyshort time period, as disclosed in a paper entitled “Development andapplication of dynamic scanning absorptometer—Automation and improvementof Bristow measurement-”, Shigenori Kuga, Japan Tappi Journal, Volume48, 1994, No. 5, pp. 730-734. The dynamic scanning absorptometerprovides an automated measurement that involves directly measuring therate of liquid absorption by tracking the motion of meniscus in acapillary, spirally scanning a liquid supply head on a disc-shapedspecimen, and automatically varying the scanning speed according to thepreset pattern to perform the measurement required number of times usinga single specimen.

The liquid supply head for supplying a liquid to a paper specimen isconnected to the capillary via a Teflon (registered trademark) tube. Theposition of meniscus is automatically tracked by an optical sensor. Inparticular, the transfer amount of pure water or ink may be measured bya dynamic scanning absorptometer K350 series D type (available fromKyowa Co., Ltd.).

The transfer amount within a contact time period of 100 ms or 400 ms isdetermined by interpolating the transfer amounts measured within contacttime periods near 100 ms or 400 ms.

Substrate

Examples of the substrate include, but are not limited to, sheet-likematerials such as wood-fiber-based paper andwood-fiber-and-synthetic-fiber-based unwoven fabric.

The paper may be made from, for example, wood pulp or used paper pulp.

Specific examples of the wood pulp include, but are not limited to,Laubholz bleached kraft pulp (LBKP), Nadelholz bleached kraft pulp(NBKP), NBSP, LBSP, GP, and TMP.

Raw materials of the used paper pulp include those listed in thematerial entitled “Quality Classification of Used Paper” issued by PaperRecycling Promotion Center (i.e., a public interest incorporatedfoundation), such as JYOUHAKU, KEIHAKU, CREAM HAKU, CARD, TOKUHAKU,CHUUHAKU, MOZOU, IROJYOU, KENT, HAKU ART, TOKUJYOUGIRI, BETSUJYOUGIRI,SHINBUN, and ZASSHI.

More specifically, raw materials of the used paper pulp include usedpaper or paperboard of printer papers (i.e., data processing papers)such as non-coated computer paper, heat-sensitive paper, andpressure-sensitive paper; office waste papers such as PPC (plain papercopier) paper; coated papers such as art paper, coat paper, fine coatingpaper, and mat paper; non-coated papers such as high quality (or woodfree) paper, high quality (or wood free) colored paper, notebook, letterpaper, wrapping paper, fancy paper, medium quality (or wood-containing)paper, newsprint paper, groundwood paper, super wrapping paper, similipaper, pure white rolled paper sheet, and milk carton. Examples of thepaper made from such pulps include, but are not limited to, chemicalpulp paper and high-yield pulp-containing paper.

Each of these materials can be used alone or in combination with others.

The used paper pulp is generally manufactured by combining the followingfour processes.

(1) Detaching process in which used paper is loosened into fibers with amechanical force and a chemical treatment by a pulper so that printingink is detached from the fibers.

(2) Dust removing process in which foreign substances (e.g., plastics)and dirt contained in the used paper are removed by a screen or cleaner.

(3) Deinking process in which the printing ink detached from the fiberswith a surfactant is removed by a flotation method or a washing method.

(4) Bleaching process in which the degree of whiteness of the fibers isenhanced by an oxidation or reduction effect.

In a case in which the used paper pulp is mixed with other pulps, themixing ratio of the used paper pulp to the total pulp is preferably 40%or less for preventing the resulting paper from curling after an imageis formed thereon.

The substrate may contain a filler. Examples of the filler include whitepigments.

Specific examples of the white pigments include, but are not limited to:white inorganic pigments such as precipitated calcium carbonate, groundcalcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate,titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white,aluminum silicate, diatom earth, calcium silicate, magnesium silicate,synthetic silica, aluminum hydroxide, alumina, lithopone, zeolite,magnesium carbonate, and magnesium hydroxide; and organic pigments suchas styrene-based plastic pigments, acrylic plastic pigments,polyethylene, microcapsule, urea resin, and melamine resin. Each ofthese pigments can be used alone or in combination with others.

When the substrate is formed into paper sheet, a sizing agent isinternally added thereto. Examples of the sizing agent for neutralpaper-making include, but are not limited to, neutral rosin-based sizingagents, alkenyl succinic anhydrides (ASA), alkyl ketene dimers (AKD),and petroleum-resin-based sizing agents. Among these, neutralrosin-based sizing agents and alkenyl succinic anhydrides arepreferable. The alkyl ketene dimers can exhibit high sizing effect in asmall amount.

Coating Layer

The coating layer contains a pigment and a binder, and optionallycontains a surfactant and other components, as necessary. In the presentdisclosure, the coating layer is not necessarily formed by means ofcoating. How to form the coating layer is not limited so long as theresultant coating layer contains a pigment and a binder.

Examples of the pigment include inorganic pigments and combinations ofinorganic and organic pigments.

Specific examples of the inorganic pigments include, but are not limitedto, kaolin, talc, ground calcium carbonate, precipitated calciumcarbonate, calcium sulfite, amorphous silica, titanium white, magnesiumcarbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide,magnesium hydroxide, zinc hydroxide, and chlorite. Among these pigments,kaolin is preferred since it has high gloss developing property and thusprovides similar texture to offset printing paper.

Examples of the kaolin include delaminated kaolin, calcined kaolin, andengineered kaolin (e.g., surface-modified kaolin). Preferably, 50% bymass or more of the total kaolin comprises kaolin particles having aparticle size distribution such that a particle diameter of 2 μm or lessaccounts for 80%, for gloss developing property.

Preferably, the content of the kaolin is 50 parts by mass or more basedon 100 parts by mass of the binder. When the content is 50 parts by massor more, glossiness is improved. There is no upper limit for the contentof kaolin. For improving coating property, the content of kaolin ispreferably 90 parts at most, considering fluidity of kaolin,particularly thickening property under high shearing force.

Specific examples of the organic pigments include, but are not limitedto, water-soluble dispersions of styrene-acrylic copolymer particles,styrene-butadiene copolymer particles, polystyrene particles, andpolyethylene particles. Two or more of the organic pigments can be usedin combination.

Preferably, the content of the organic pigment is 2 to 20 parts by massbased on 100 parts by mass of the total pigments in the coating layer.The organic pigment is bulky and highly glossy for its excellent glossdeveloping property and smaller specific weight than the inorganicpigments. Therefore, the organic pigment can provide a coating layerhaving high gloss and surface coating property. When the content is 2parts by mass or more, the above effect is more improved. When thecontent is 20 parts by mass or less, the coating liquid exhibitsexcellent fluidity, which improves coating operability while reducingcost.

The organic pigment may be in the form of a dense solid, hallow, ordonut. For achieving a good balance between gloss developing property,surface coating property, and fluidity of the coating liquid,preferably, the organic pigment has an average particle diameter of from0.2 to 3.0 μm and has a hollow shape having a void area ratio of 40% ormore.

Preferably, the binder comprises a water-based resin.

The water-based resin includes both water-soluble resins andwater-dispersible resins.

Specific examples of the water-soluble resins include, but are notlimited to: polyvinyl alcohol and modified products thereof, such asanion-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, andacetal-modified polyvinyl alcohol; polyurethane; polyvinyl pyrrolidoneand modified products thereof, such as copolymer of polyvinylpyrrolidone and vinyl acetate, copolymer of vinyl pyrrolidone anddimethylaminoethyl methacrylic acid, copolymer of quaternized vinylpyrrolidone and dimethylaminoethyl methacrylic acid, and copolymer ofvinyl pyrrolidone and methacrylamide propyl trimethyl ammonium chloride;celluloses such as carboxymethyl cellulose, hydroxyethyl cellulose, andhydroxypropyl cellulose; modified celluloses such as cationizedhydroxyethyl cellulose; synthetic resins such as polyester, polyacrylicacid, polyacrylate, melamine resin, and modified products thereof, andcopolymer of polyester and polyurethane; polyacrylic acid andpolymethacrylic acid; polyacrylamide and polymethacrylamide; modifiedstarches such as oxidized starch, phosphoric-acid-esterified starch,self-modified starch, and cationized starch; polyethylene oxides; andsodium polyacrylate and sodium alginate. Each of these resins can beused alone or in combination with others.

Among these resins, polyvinyl alcohol, cation-modified polyvinylalcohol, acetal-modified polyvinyl alcohol, polyester, polyurethane, andcopolymer of polyester and polyurethane are preferable for inkabsorptivity.

Specific examples of the water-dispersible resins include, but are notlimited to, polyvinyl acetate, ethylene-vinyl acetate copolymer,polystyrene, copolymer of styrene with acrylate or methacrylate,acrylate or methacrylate polymer, copolymer of vinyl acetate withacrylic acid, methacrylic acid, acrylate, or methacrylate,styrene-butadiene copolymer, ethylene-propylene copolymer, polyvinylether, and silicone-acrylic copolymer. In addition, thewater-dispersible resin may contain a cross-linker, such as methylolmelamine, methylol urea, methylol hydroxypropylene urea, and isocyanate.Alternatively, the water-dispersible resin may be a self-cross-linkablecopolymer having an N-methylol acrylamide unit. Each of thesewater-dispersible resins can be used alone or in combination withothers.

The content of the water-dispersible resin is preferably in the range offrom 2 to 100 parts by mass, more preferably from 3 to 50 parts by mass,based on 100 parts by mass of the pigment. The content is determined sothat the liquid absorption property of the recording medium falls intothe above-specified range.

The coating layer may contain a cationic organic compound. Examples ofthe cationic organic compound include monomers, oligomers, and polymersof primary, secondary, and tertiary amines and quaternary ammonium saltsthat react with sulfonic acid group, carboxyl group, amino group, etc.in a direct dye or acid dye contained in the ink.

Specific examples of the cationic organic compound include, but are notlimited to, dimethylamine-epichlorohydrin polycondensate,dimethylamine-ammonia-epichlorohydrin condensate,poly(trimethylaminoethyl methacrylate-methyl sulfate), diallylaminehydrochloride-acrylamide copolymer, poly(diallylaminehydrochloride-sulfur dioxide), polyallylamine hydrochloride,poly(allylamine hydrochloride-diallylamine hydrochloride),acrylamide-diallylamine copolymer, polyvinylamine copolymer,dicyandiamide, dicyandiamide-ammonium chloride-urea-formaldehydecondensate, polyalkylenepolyamine-dicyandiamide ammonium saltcondensate, dimethyldiallylammonium chloride, polydiallylmethylaminehydrochloride, poly(diallyldimethylammonium chloride),poly(diallyldimethylammonium chloride-sulfur dioxide),poly(diallyldimethylammonium chloride-diallylamine hydrochloridederivative), acrylamide-diallyldimethylammonium chloride copolymer,acrylate-acrylamide-diallylamine hydrochloride copolymer,polyethyleneimine, ethyleneimine derivatives such as acrylamine polymer,and alkylene-oxide-modified polyethyleneimine. Each of these compoundscan be used alone or in combination with others.

In particular, combination use of a low-molecular-weight cationicorganic compound, such as dimethylamine-epichlorohydrin polycondensateand polyarylamine hydrochloride, with a relatively-high-molecular-weightcationic organic compound, such as poly(diallyldimethylammoniumchloride), is preferable. The combination use more improves imagedensity and suppresses feathering compared to sole use.

Preferably, the cationic organic compound has a cation equivalent offrom 3 to 8 meq/g, when measured by a colloid titration method (usingpotassium polyvinyl sulfate and tolidine blue). When the cationequivalent is within the above range, good results will be obtained aslong as the deposition amount of the cationic organic compound afterbeing dried is within the preferred range described later.

In measuring cation equivalent by the colloid titration method, thecationic organic compound is diluted with purified water so that solidcontent concentration becomes 0.1% by mass without adjusting pH.

Preferably, the deposition amount of the cationic organic compound afterbeing dried is from 0.3 to 2.0 g/m². When the deposition amount of thecationic organic compound after being dried is from 0.3 to 2.0 g/m²,image density is more improved and feathering is more suppressed.

Examples of the surfactant include anionic surfactants, cationicsurfactants, ampholytic surfactants, and nonionic surfactants. Amongthese, nonionic surfactants are preferable. As the surfactant iscontained in the coating layer, water resistance and density of theimage are improved and bleeding is suppressed.

Specific examples of the nonionic surfactants include, but are notlimited to, ethylene oxide adducts of higher alcohols, ethylene oxideadducts of alkyl phenols, ethylene oxide adducts of fatty acids,ethylene oxide adducts of polyol fatty acid esters, ethylene oxideadducts of higher aliphatic amines, ethylene oxide adducts of fatty acidamides, ethylene oxide adducts of oils and fats, ethylene oxide adductsof polypropylene glycol, fatty acid esters of glycerol, fatty acidesters of pentaerythritol, fatty acid esters of sorbitol or sorbitan,fatty acid esters of sucrose, alkyl ethers of polyols, and fatty acidamides of alkanolamines. Each of these compounds can be used alone or incombination with others.

Specific examples of the polyols include, but are not limited to,glycerol, trimethylolpropane, pentaerythritol, sorbitol, and sucrose.

With respect to the ethylene oxide adducts, a part of the ethyleneoxides may be replaced with other alkylene oxides such as propyleneoxide and butylene oxide so long as water-solubility is maintained. Inthis case, preferably, the replacement ratio is 50% or less.

The HLB (Hydrophilic-Lipophilic Balance) of the nonionic surfactant ispreferably from 4 to 15, more preferably from 7 to 13.

The addition amount of the surfactant is preferably from 0 to 10 partsby mass, more preferably from 0.1 to 1.0 parts by mass, based on 100parts by mass of the cationic organic compound.

The coating layer may further contain other components withoutcompromising the effect thereof. Examples of other components include,but are not limited to, additives such as alumina powder, pH adjuster,preservative, and antioxidant.

There is no limit on how to form the coating layer. For example, thecoating layer may be formed by impregnating or coating the substratewith the coating liquid. The substrate may be impregnated or coated withthe coating liquid by a coater such as conventional size press, gateroll size press, film transfer size press, blade coater, rod coater, airknife coater, and curtain coater. For reducing cost, the substrate maybe first impregnated or coated with the coating liquid by a conventionalsize press, gate roll size press, or film transfer size press installedin a paper machine, and finished on-machine.

The deposition amount of the coating liquid is preferably from 0.5 to 20g/m², more preferably from 1 to 15 g/m², based on solid contents.

The substrate impregnated or coated with the coating liquid may besubject to drying, if needed. The drying temperature is preferably from100° C. to 250° C., but is not limited thereto.

The recording medium may further comprise a back layer on the back sideof the substrate, a layer between the substrate and the coating or backlayer, and/or a protective layer on the coating layer. Each of theselayers may be either single-layered or multi-layered.

Pressurizing Process and Pressurizer

The pressurizing process is a process in which a pressure is applied tothe recording medium to which the ink has been applied in the first inkapplying process.

The pressurizer is configured to apply a pressure to the recordingmedium to which the ink has been applied by the first ink applier.

The pressurizing process is preferably performed by the pressurizer.

Preferably, in the pressurizing process, the pressure is generated asthe continuous sheet to which the ink has been applied is wound in aroll.

In addition to such a case in which the continuous sheet is stacked inlayers, the pressure may be generated as cut sheets are stacked inlayers or the continuous or cut sheet is cut. The pressure may also beapplied to the sheet from a fixing roller for fixing the image and anapplication roller for applying an aftertreatment liquid to the image.

Second Ink Applying Process and Second Ink Applier

The second ink applying process is a process in which an ink is appliedto the continuous sheet to form another image after the pressurizingprocess.

The second ink applier is configured to apply an ink to the continuoussheet to form another image after the pressurizing process.

The second ink applying process is preferably performed by the secondink applier.

Method for Manufacturing Printed Matter

In accordance with some embodiments of the present invention, a methodfor manufacturing printed matter is provided that includes the steps of:(a) applying an ink to a recording medium to form an image (hereinafter“first ink applying process”); and (b) applying a pressure to therecording medium to which the ink has been applied (hereinafter“pressurizing process”). The ink comprises water, an organic solvent,and a colorant. When the ink is formed into an ink film, a maximum valueof logarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C. The pressure may be in the range of from 3.5 to 8.0 kg/cm². Thepressure may be generated as the recording medium to which the ink hasbeen applied is wound in a roll.

The first ink applying process may be the same as the first ink applyingprocess in the above-described image forming method.

The pressurizing process may be the same as the pressurizing process inthe above-described image forming method.

Hereinafter, the image forming method, image forming apparatus, imageforming system, and method for manufacturing printed matter inaccordance with some embodiments of the present invention are describedwith reference to the drawings. In the present disclosure, the imageforming system is defined as a concept including multiple apparatuseswhen each constitutional elements of the invention exists in each of themultiple apparatuses or extends over some of the multiple apparatuses.For example, the concept includes a case in which the first ink applierand the pressurizer exist in separate apparatuses. In the presentdisclosure, the continuous sheet is defined as a recording medium thatis continuous in the direction of conveyance in image formation.

Examples of the continuous sheet include rolled sheet (rolled in a rollform) and folded sheet (folded at predetermined interval). Incidentally,it is to be noted that the following embodiments are not limiting thepresent disclosure and any deletion, addition, modification, change,etc. can be made within a scope in which man in the art can conceiveincluding other embodiments, and any of which is included within thescope of the present disclosure as long as the effect and feature of thepresent disclosure are demonstrated.

FIG. 3 is a schematic view of an image forming apparatus in accordancewith some embodiments of the present invention, which is an inkjetrecording apparatus. An inkjet recording apparatus 300 includes arecording medium conveyer 301, a pretreatment unit 302 to apply apretreatment liquid to a recording medium 203, a post-pretreatment dryer303 to dry the recording medium 203 to which the pretreatment liquid hasbeen applied, an image forming unit 304, an aftertreatment unit 305 toapply an aftertreatment liquid to the recording medium 203 on which animage has been formed, and a post-aftertreatment dryer 306 to dry therecording medium 203 to which the aftertreatment liquid has beenapplied.

The recording medium conveyer 301 includes a sheet feeder 307, multipleconveyance rollers, and a winder 308. The recording medium 203 is acontinuous sheet wound in a roll (i.e., rolled sheet). The recordingmedium 203 is wound off from the sheet feeder 307 by the conveyanceroller, conveyed on a platen, and wound up by the winder 308.

In the pretreatment unit 302, a pretreatment liquid is applied to therecording medium 203 conveyed by the recording medium conveyer 301.Generally, if a recording medium non-exclusively for inkjet printing isused for inkjet image forming apparatus, various problems regardingimage quality (e.g., blurring, density, color tone, bleed-through) orimage toughness (e.g., water resistance, fade resistance) will arise. Tosolve these problems and improve image quality, the pretreatment liquidhaving a function of aggregating ink is previously applied to therecording medium before an image is formed thereon.

In the pretreatment unit 302, the pretreatment liquid is uniformlyapplied to the surface of the recording medium 203 by any knownapplication method. Specific examples of the application method include,but are not limited to, blade coating, gravure coating, gravure offsetcoating, bar coating, roll coating, knife coating, air knife coating,comma coating, U comma coating, AKKU coating, smoothing coating, microgravure coating, reverse roll coating, 4-roll or 5-roll coating, dipcoating, curtain coating, slide coating, and die coating.

The post-pretreatment dryer 303 is disposed downstream from thepretreatment unit 302. The post-pretreatment dryer 303 includes heatrollers 311 and 312. The recording medium 203 to which the pretreatmentliquid has been applied is conveyed to the heat rollers 311 and 312 byconveyance rollers. The heat rollers 311 and 312 are heated to a hightemperature of from 50° C. to 100° C. Thus, as the recording medium 203to which the pretreatment liquid has been applied contacts the heatrollers 311 and 312, moisture is evaporated from the recording medium203 by transmission of heat, thus drying the recording medium 203.

FIG. 4 is a magnified view of a recording head 304K included in theimage forming unit 304 illustrated in FIG. 3. The recording head 304Khas a nozzle surface 309 on which multiple printing nozzles 310 arearranged in the longitudinal direction of the recording head 304K toform a nozzle array. In the present embodiment, only one nozzle array isprovided for an illustrative purpose. The number of nozzle arrays is notlimited to one. The image forming unit 304 includes four recording heads304K, 304C, 304M, and 304Y Each of the recording heads 304C, 304M, and304Y has the same configuration as the recording head 304K. The fourrecording heads 304K, 304C, 304M, and 304Y are arranged at regularintervals in the direction of conveyance of the recording medium 203.This configuration makes it possible to form an image over the entireprinting area through one time of printing operation.

In the aftertreatment unit 305 disposed downstream from the imageforming unit 304, an aftertreatment liquid is applied to the recordingmedium 203. The aftertreatment liquid contains a component capable offorming a transparent protective layer on the recording medium 203.

In the aftertreatment unit 305, the aftertreatment liquid is appliedonly to a specific part of the image forming region on the recordingmedium 203. Preferably, the application amount of the aftertreatmentliquid is adjusted depending on the color of the ink forming an image.More preferably, the application amount and application method of theaftertreatment liquid are varied depending on the type of recordingmedium and image resolution.

There is no particular limitation on the method of applying theaftertreatment liquid, and various methods are appropriately selecteddepending the type of the aftertreatment liquid. Preferably, theabove-described method of applying the pretreatment liquid or jettingink is used for applying the aftertreatment liquid. From the viewpointof apparatus configuration and storage stability of the aftertreatmentliquid, the method of jetting ink is more preferably used therefor. Theaftertreatment process is a process in which the aftertreatment liquidcontaining a transparent resin is applied to the surface of the image toform a protective layer such that the deposition amount of theaftertreatment liquid when being dried becomes in the range of from 0.5to 10 g/m².

The post-aftertreatment dryer 306 includes heat rollers 313 and 314. Therecording medium 203 to which the aftertreatment liquid has been appliedis conveyed to the heat rollers 313 and 314 by conveyance rollers. Theheat rollers 313 and 314 are heated to a high temperature. Thus, as therecording medium 203 to which the aftertreatment liquid has been appliedcontacts the heat rollers 313 and 313, moisture is evaporated from therecording medium 203 by transmission of heat, thus drying the recordingmedium 203. The configuration of the post-aftertreatment dryer 306 isnot limited to the above-described configuration. Thepost-aftertreatment dryer 306 may include an infrared dryer, microwavedryer, hot air device, or combination thereof (e.g., combination of aheat roller and a hot air device).

EXAMPLES

Further understanding can be obtained by reference to certain specificexamples which are provided herein for the purpose of illustration onlyand are not intended to be limiting.

In the following Examples and Comparative Examples, the maximum value oflogarithmic damping ratio and the time elapsed until the logarithmicdamping ratio reaches the maximum value were measured as follows.

Maximum Value of Logarithmic Damping Ratio/Time Elapsed UntilLogarithmic Damping Ratio Reaches Maximum Value

The maximum value of logarithmic damping ratio and the time elapseduntil the logarithmic damping ratio reaches the maximum value weremeasured with a Rigid-body Pendulum Type Physical Properties TestingInstrument RPT-3000W (available from A&D Company, Limited).

Specifically, an ink film was formed by dropping 40 μL of the ink ontoan aluminum substrate and forming the dropped ink into a film having athickness of 100 μm using a coating jig (PCT-100). The ink film wasimmediately set along with a cold block (CHB-100). A cylinder edge(RBP-040) and a pendulum (FRB-100) were set up, and two weightsexclusive for FRB-100 were set at the lowest part of the pendulum. Themeasurement temperature was raised from normal temperature (25° C.) to60° C. at a rate of 5° C./min and kept at 60° C. thereafter. Thelogarithmic damping ratio and temperature were plotted along the time.The obtained curve was smoothened and the maximum value thereof wascalculated as the maximum value of logarithmic damping ratio.

A logarithmic damping ratio (D′(n)) after the smoothing was determinedfrom the following formulae, where D(n) representing logarithmic dampingratio of the n^(th) plot.D′(n)={D(n−2)+D(n−1)+D(n)+D(n+1)+D(n+2)}/5D′(1)=D(1)D′(2)={D(1)+D(2)}/2

Polyurethane Resin Particle Dispersion Liquid Preparation Example 1

Preparation of Polyurethane Resin Particle Dispersion Liquid 1

In a reaction vessel equipped with a cooling tube, a stirrer, and anitrogen inlet tube, 1,6-hexanediol and 1,6-hexanedioic acid were pouredso that the ratio OH/COOH became 1.5, along with titaniumtetraisopropoxide in an amount 1,000 ppm (1% by mass) based on resincomponents. The temperature was thereafter raised to 200° C. over aperiod of 4 hours. The temperature was further raised to 230° C. over aperiod of 2 hours. The reaction was continued until no water outflowed.The reaction was further continued under reduced pressures of from 1,334to 2,000 Pa (i.e., 10 to 15 mmHg) for 5 hours. Thus, an intermediatepolyester was obtained.

Next, in a reaction vessel equipped with a cooling tube, a stirrer, anda nitrogen inlet tube, the intermediate polyester and isophoronediisocyanate were poured so that the molar ratio became 2.0, dilutedwith ethyl acetate so that the concentration became 48% by mass, andreacted at 100° C. for 5 hours. A large amount of water was furtherpoured in the vessel and the solvent was removed. Thus, a polyurethaneresin particle dispersion liquid 1 having a solid content concentrationof 10% by mass was prepared.

Polyurethane Resin Particle Dispersion Liquid Preparation Example 2

Preparation of Polyurethane Resin Particle Dispersion Liquid 2

The procedure in Polyurethane Resin Particle Dispersion LiquidPreparation Example 1 was repeated except for replacing the1,6-hexanediol with 1,4-butanediol. Thus, a polyurethane resin particledispersion liquid 2 having a solid content concentration of 10% by masswas prepared.

Polyurethane Resin Particle Dispersion Liquid Preparation Example 3

Preparation of Polyurethane Resin Particle Dispersion Liquid 3

The procedure in Polyurethane Resin Particle Dispersion LiquidPreparation Example 1 was repeated except for replacing the1,6-hexanedioic acid with 1,4-butanedioic acid. Thus, a polyurethaneresin particle dispersion liquid 3 having a solid content concentrationof 10% by mass was prepared.

Ink Preparation Example 1

Preparation of Ink 1

An ink 1 was prepared by stir-mixing 5.0% by mass of a magenta pigment(Pigment Red 122 available from Dainichiseika Color & Chemicals Mfg.Co., Ltd.), 4.0% by mass of tripropylene glycol monobutyl ether(available from Dow Chemical Japan Limited), 5.0% by mass of triethyleneglycol dimethyl ether (available from Dow Chemical Japan Limited), 25.0%by mass of 1,2-propanediol (also known as propylene glycol, availablefrom Kanto Chemical Co., Inc.), 50.0% by mass of the polyurethane resinparticle dispersion liquid 1 (having a solid content concentration of10% by mass), and ultrapure water in a residual amount such that thetotal percentage became 100% by mass. Thus, an ink 1 was prepared.

Ink Preparation Examples 2 to 20

Preparation of Inks 2 to 20

The procedure in Ink Preparation Example 1 was repeated except forchanging the composition according to the formulations described inTables 1 to 3. Thus, inks 2 to 20 were prepared.

TABLE 1 Ink 1 2 3 4 5 6 7 Colorant Magenta pigment 5.0 5.0 5.0 5.0 5.05.0 5.0 Yellow pigment — — — — — — — Organic Tripropylene glycolmonobutyl ether 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Solvent Triethylene glycoldimethyl ether 5.0 — — — 5.0 — — Diethylene glycol diethyl ether — 5.0 —— — 5.0 — Dipropylene glycol dimethyl ether — — 5.0 — — — 5.0Tripropylene glycol dimethyl ether — — — 5.0 — — — 1,2-Propanediol 25.025.0 25.0 25.0 25.0 25.0 25.0 Resin Polyurethane resin particledispersion 50.0 50.0 50.0 50.0 — — — liquid 1 Polyurethane resinparticle dispersion — — — — 50.0 50.0 50.0 liquid 2 Polyurethane resinparticle dispersion — — — — — — — liquid 3 Water Ultrapure waterResidual Residual Residual Residual Residual Residual Residual AmountAmount Amount Amount Amount Amount Amount Total (% by mass) 100 100 100100 100 100 100 Mass Ratio 1.8 1.8 1.8 1.8 1.8 1.8 1.8 (Glycol ethercompound/Urethane resin particles)

TABLE 2 Ink 8 9 10 11 12 13 14 Colorant Magenta pigment 5.0 5.0 5.0 5.05.0 5.0 5.0 Yellow pigment — — — — — — — Organic Tripropylene glycolmonobulyl ether 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Solvent Triethylene glycoldimethyl ether — 5.0 — — — — — Diethylene glycol diethyl ether — — 5.0 —— — — Dipropylene glycol dimethyl ether — — — 5.0 — 2.0 8.0 Tripropyleneglycol dimethyl ether 5.0 — — — 5.0 — — 1,2-Propanediol 25.0 25.0 25.025.0 25.0 25.0 25.0 Resin Polyurethane resin particle dispersion — — — —— — — liquid 1 Polyurethane resin particle dispersion 50.0 — — — — — —liquid 2 Polyurethane resin particle dispersion — 50.0 50.0 50.0 50.050.0 50.0 liquid 3 Water Ultrapure water Residual Residual ResidualResidual Residual Residual Residual Amount Amount Amount Amount AmountAmount Amount Total (% by mass) 100 100 100 100 100 100 100 Mass Ratio1.8 1.8 1.8 1.8 1.8 1.2 2.4 (Glycol ether compound/Urethane resinparticles)

TABLE 3 Ink 15 16 17 18 19 20 Colorant Magenta pigment — 5.0 5.0 5.0 5.05.0 Yellow pigment 5.0 — — — — — Organic Tripropylene glycol monobutylether 4.0 4.0 4.0 4.0 4.0 4.0 Solvent Triethylene glycol dimethyl ether— — — — — — Diethylene glycol diethyl ether — — — — — — Dipropyleneglycol dimethyl ether 5.0 — — — 1.8 8.2 Tripropylene glycol dimethylether — — — — — — 1,2-Propanediol 25.0 25.0 25.0 25.0 25.0 25.0 ResinPolyurethane resin particle dispersion — 50.0 — — — — liquid 1Polyurethane resin particle dispersion — — 50.0 — — — liquid 2Polyurethane resin particle dispersion 50.0 — — 50.0 50.0 50.0 liquid 3Water Ultrapure water Residual Residual Residual Residual ResidualResidual Amount Amount Amount Amount Amount Amount Total (% by mass) 100100 100 100 100 100 Mass Ratio 1.8 0.8 0.8 0.8 1.2 2.4 (Glycol ethercompound/Urethane resin particles)

The product names and manufacturers of the materials described in Tables1 to 3 are listed below.

Magenta pigment: Pigment Red 122 available from Dainichiseika Color &Chemicals Mfg. Co., Ltd.

Yellow pigment: Pigment Yellow 154 available from Dainichiseika Color &Chemicals Mfg. Co., Ltd.

Tripropylene glycol monobutyl ether: available from Dow Chemical JapanLimited

Triethylene glycol dimethyl ether: available from Dow Chemical JapanLimited

Diethylene glycol diethyl ether: available from Dow Chemical JapanLimited

Dipropylene glycol dimethyl ether: available from Dow Chemical JapanLimited

Tripropylene glycol dimethyl ether: available from Dow Chemical JapanLimited

1,2-Propanediol (Propylene glycol): available from Kanto Chemical Co.,Inc.

Examples 1 to 39 and Comparative Examples 1 to 10

Image Formation

An inkjet printing system (RICOH Pro VC60000 available from Ricoh Co.,Ltd.) was loaded with each of the inks 1 to 20. Images were formed bythis system on both sides of a recording medium and subjected toevaluations. As the recording medium, LAG90 (available from Stora Enso,having a width of 520.7 mm), Magno Plus Silk (available from SappiGlobal), and Mango Gloss (available from Sappi Global) were used asshown in Tables 4 and 5, each of which being a rolled sheet. Each rolledsheet was set in the printing system and a solid image having aresolution of 1,200 dpi was recorded thereon. As the winder, a RewindingModule RW6 (available from Hunkler) was used. The winder performedwinding of the sheet so that the pressure was adjusted as shown inTables 4 and 5 by simply stacking the sheet. The image was subjected tothe evaluations in terms of blocking resistance, abrasion resistance,and glossiness. Next, the recording medium having the image thereon wasset in the printing system again. Another solid image having aresolution of 1,200 dpi was recorded thereon after replacing the ink(“first ink”) with a black ink (“second ink”). The image was subjectedto the evaluation of position misalignment at the second inkapplication. The pressure applied to the image on the recording mediumwas measured by a surface pressure distribution measuring system I-SCAN(available from Nitta Corporation) and a sensor sheet I-SCAN #5027(available from Nitta Corporation). More specifically, as illustrated inFIGS. 5 and 6, a continuous sheet 12 was wound in a roll and sensorsheets 13 were placed at the positions 20 cm away from the outside of apaper core 11 having a hollow 10. The three sensor sheets 13 were placedat different positions relative to the width direction of the continuoussheet 12, thus setting three measuring points. Winding of the continuoussheet 12 was continued until the sheet stacked above the three measuringpoints came to have a thickness of 10 cm. At this time, the pressure wasmeasured at each measuring points. The pressure values measured at thethree measuring points were averaged to determine the pressure appliedto the image. The evaluation results are shown in Tables 4 and 5.

With respect to LAG90, the transfer amount of pure water within contacttimes of 100 ms and 400 ms are 2.9 mL/m² and 4.9 mL/m², respectively,when measured by the dynamic scanning absorptometer (“DSA”) disclosed ina paper entitled “Development and application of dynamic scanningabsorptometer—Automation and improvement of Bristow measurement-”,Shigenori Kuga, Japan Tappi Journal, Volume 48, 1994, No. 5, pp.730-734.

With respect to Mango Plus Silk, the transfer amount of pure waterwithin contact times of 100 ms and 400 ms are 2.5 mL/m² and 4.3 mL/m²,respectively, when measured by the dynamic scanning absorptometer(“DSA”) disclosed in a paper entitled “Development and application ofdynamic scanning absorptometer—Automation and improvement of Bristowmeasurement-”, Shigenori Kuga, Japan Tappi Journal, Volume 48, 1994, No.5, pp. 730-734.

With respect to Mango Gloss, the transfer amount of pure water withincontact times of 100 ms and 400 ms are 1.8 mL/m² and 3.5 mL/m²,respectively, when measured by the dynamic scanning absorptometer(“DSA”) disclosed in a paper entitled “Development and application ofdynamic scanning absorptometer—Automation and improvement of Bristowmeasurement-”, Shigenori Kuga, Japan Tappi Journal, Volume 48, 1994, No.5, pp. 730-734.

Blocking Resistance

The sheet was visually observed to determine the degree of stickingbetween images and the degree of image transfer (offset). Blockingresistance was evaluated based on the following evaluation criteria.Rank 7 or more are good quality. Rank 10 is the best quality. Rank 3 orless is significantly poor quality.

Evaluation Criteria

10: Sheets were not sticking together. No image peeling was observed.Visually uniform image.

9: Sheets were not sticking together. No image peeling observed. Smallimage void less than 10 μm was observed.

8: Sheets were not sticking together. No image peeling observed. Smallimage void less than 20 μm but not less than 10 μm was observed.

7: Sheets were not sticking together. No image peeling observed. Smallimage void less than 30 μm but not less than 20 μm was observed.

6: Sheets were not sticking together. No image peeling observed. Smallimage void less than 40 μm but not less than 30 μm was observed.

3: Sheets were sticking together. Significant image missing wasobserved.

1: Sheets were sticking together. Significant image missing and sheetmissing were observed.

0: Sheets were sticking together and united.

Abrasion Resistance

Each image was rubbed with a 1.2-cm-square piece of paper (LAG90available from Stora Enso) 20 times. Image density of the paper wasmeasured thereafter by a reflective color spectrophotometricdensitometer (available from X-Rite) and the background image density ofthe paper was subtracted therefrom to determine the transferred inkdensity. Abrasion resistance was evaluated based on the followingevaluation criteria.

Evaluation Criteria

A: The transferred ink density was less than 0.05.

B: The transferred ink density was not less than 0.05 and less than0.10.

C: The transferred ink density was not less than 0.10.

Glossiness

Each image was subjected to a measurement of 600 gloss by a gloss meter(Micro-TRI-Gloss 4520 available from BYK Gardner) before and after beingpressurized.

Position Misalignment at Second Ink Application

The image was visually observed to determine whether positionmisalignment had occurred in the second ink application relative to thefirst ink application.

Evaluation Criteria

A: Position misalignment did not occur

C: Position misalignment occurred.

TABLE 4 Logarithmic damping ratio Evaluation results Elapsed GlossPosition Ink Recording Maximum time Pressure Blocking Abrasion BeforeAfter Mis- No. medium value (sec) (kg/cm²) resistance resistancePressure Pressure alignment Examples 1 1 LAG90 1.50 3,800 8.0 7 A 31 41A 2 LAG90 7.3 8 A 40 A 3 LAG90 5.8 8 A 39 A 4 LAG90 4.6 9 A 38 A 5 LAG903.5 9 A 38 A 6 2 LAG90 1.48 3,600 8.0 8 A 31 41 A 7 LAG90 3.5 9 A 39 A 83 LAG90 1.40 3,400 8.0 9 A 31 41 A 9 LAG90 3.5 10 A 39 A 10 4 LAG90 1.453,200 8.0 9 A 31 41 A 11 LAG90 3.5 10 A 39 A 12 5 LAG90 1.35 3,700 8.0 8A 31 41 A 13 LAG90 3.5 9 A 39 A 14 6 LAG90 1.33 3,500 8.0 8 A 31 41 A 15LAG90 3.5 9 A 39 A 16 7 LAG90 1.26 3,300 8.0 10 A 31 41 A 17 LAG90 3.510 A 39 A 18 8 LAG90 1.31 3,100 8.0 9 A 31 41 A 19 LAG90 3.5 10 A 39 A20 9 LAG90 0.75 2,500 8.0 9 A 32 42 A 21 LAG90 3.5 10 A 40 A 22 10 LAG900.74 2,000 8.0 9 A 32 42 A 23 LAG90 3.5 10 A 40 A 24 11 LAG90 0.70 1,8008.0 10 A 32 42 A 25 LAG90 3.5 10 A 40 A 26 12 LAG90 0.73 1,700 8.0 10 A32 42 A 27 LAG90 3.5 10 A 40 A 28 13 LAG90 0.93 3,300 8.0 8 A 32 42 A 29LAG90 3.5 10 A 40 A 30 14 LAG90 1.33 3,400 8.0 9 A 32 42 A 31 LAG90 3.510 A 40 A 32 15 LAG90 0.71 1,900 8.0 10 A 32 42 A 33 LAG90 3.5 10 A 40 A

TABLE 5 Logarithmic damping ratio Evaluation results Elapsed GlossPosition Ink Recording Maximum time Pressure Blocking Abrasion BeforeAfter Mis- No. medium value (sec) (kg/cm²) resistance resistancePressure Pressure alignment Examples 34 11 Magno 0.70 1,800 8.0 10 A 3749 A Plus Silk 35 Magno 3.5 10 A 44 A Plus Silk 36 11 Magno 0.70 1,8008.0 10 A 35 47 A Gloss 37 Magno 3.5 10 A 41 A Gloss 38 1 LAG90 1.503,800 8.2 6 A 31 — A 39 LAG90 3.1 10 B 39 C Comparative 1 16 LAG90 3.705,000 8.0 0 A 31 — A Examples 2 LAG90 3.5 0 A — A 3 17 LAG90 2.42 4,9008.0 0 A 31 — A 4 LAG90 3.5 1 A — A 5 18 LAG90 2.10 4,200 8.0 0 A 32 — A6 LAG90 3.5 1 A — A 7 19 LAG90 1.11 3,900 8.0 0 A 32 — A 8 LAG90 3.5 3 A— A 9 20 LAG90 1.62 3,700 8.0 0 A 32 — A 10 LAG90 3.5 3 A — A

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it will be obvious that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

The invention claimed is:
 1. An image forming method comprising: (a)applying an ink to a recording medium to form an image; and (b) applyinga pressure to the recording medium to which the ink has been applied,wherein the ink comprises water, an organic solvent, and a colorant,wherein, when the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C.
 2. The image forming method of claim 1, wherein the pressure instep (b) is in the range of from 3.5 to 8.0 kg/cm².
 3. The image formingmethod of claim 2, wherein the recording medium is a continuous sheet,wherein step (b) includes winding the recording medium in a roll.
 4. Theimage forming method of claim 3, further comprising: (c) applying an inkto the recording medium to form another image after step (b).
 5. Theimage forming method of claim 2, wherein the recording medium includes asubstrate and a coating layer on at least one surface of the substrate,wherein a transfer amount of pure water to the recording medium within acontact time of 100 ms is from 2 to 35 mL/m² and that within a contacttime of 400 ms is from 3 to 40 mL/m², when measured by a dynamicscanning absorptometer.
 6. The image forming method of claim 2, whereinthe ink further comprises urethane resin particles.
 7. The image formingmethod of claim 2, wherein the organic solvent comprises a glycol ethercompound.
 8. The image forming method of claim 7, wherein the glycolether compound has no hydroxyl group.
 9. The image forming method ofclaim 1, wherein the recording medium is a continuous sheet, whereinstep (b) includes winding the recording medium in a roll.
 10. The imageforming method of claim 9, further comprising: (c) applying an ink tothe recording medium to form another image after step (b).
 11. The imageforming method of claim 9, wherein the recording medium includes asubstrate and a coating layer on at least one surface of the substrate,wherein a transfer amount of pure water to the recording medium within acontact time of 100 ms is from 2 to 35 mL/m² and that within a contacttime of 400 ms is from 3 to 40 mL/m², when measured by a dynamicscanning absorptometer.
 12. The image forming method of claim 1, whereinthe recording medium includes a substrate and a coating layer on atleast one surface of the substrate, wherein a transfer amount of purewater to the recording medium within a contact time of 100 ms is from 2to 35 mL/m² and that within a contact time of 400 ms is from 3 to 40mL/m², when measured by a dynamic scanning absorptometer.
 13. The imageforming method of claim 1, wherein the ink further comprises urethaneresin particles.
 14. The image forming method of claim 1, wherein theorganic solvent comprises a glycol ether compound.
 15. The image formingmethod of claim 14, wherein the glycol ether compound has no hydroxylgroup.
 16. The image forming method of claim 15, wherein the glycolether compound is represented by the following formula (1):

where R¹ represents a hydrogen atom or alkyl group having 1 to 10 carbonatoms, each of R² and R³ independently represents an alkyl group having1 to 10 carbon atoms, and n represents an integer of from 1 to
 5. 17.The image forming method of claim 14, wherein the ink further comprisesurethane resin particles, wherein a mass ratio of the glycol ethercompound to the urethane resin particles is in the range of from 0.4 to1.8.
 18. The image forming method of claim 14, wherein the glycol ethercompound accounts for 2.0% to 8.0% by mass of the ink.
 19. The imageforming method of claim 1, wherein the maximum value of logarithmicdamping ratio of the ink film is from 0.01 to 1.30 and the time elapseduntil the logarithmic damping ratio reaches the maximum value is from100 to 3,000 seconds, when measured by the rigid-body pendulum test at60° C.
 20. A method of manufacturing printed matter comprising: (a)applying an ink to a recording medium to form an image; and (b) applyinga pressure to the recording medium to which the ink has been applied,wherein the ink comprises water, an organic solvent, and a colorant,wherein, when the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C.
 21. An ink comprising: water; an organic solvent; and a colorant,wherein, when the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C.
 22. The ink of claim 21, further comprising: urethane resinparticles.
 23. The ink of claim 21, wherein the organic solventcomprises a glycol ether compound.
 24. The ink of claim 23, furthercomprising: urethane resin particles, wherein a mass ratio of the glycolether compound to the urethane resin particles is in the range of from0.4 to 1.8.
 25. The ink of claim 21, wherein the maximum value oflogarithmic damping ratio of the ink film is from 0.01 to 1.30 and thetime elapsed until the logarithmic damping ratio reaches the maximumvalue is from 100 to 3,000 seconds, when measured by the rigid-bodypendulum test at 60° C.
 26. An image forming method comprising: (a)applying an ink to a continuous sheet to form an image; and (b) windingthe continuous sheet to which the ink has been applied into a roll,wherein the ink comprises water, an organic solvent, and a colorant,wherein, when the ink is formed into an ink film, a maximum value oflogarithmic damping ratio of the ink film is 1.50 or less and a timeelapsed until the logarithmic damping ratio reaches the maximum value is3,800 seconds or less, when measured by a rigid-body pendulum test at60° C.
 27. The image forming method of claim 26, further comprising: (c)applying an ink to the continuous sheet to form another image after step(b).
 28. The image forming method of claim 26, wherein the recordingmedium includes a substrate and a coating layer on at least one surfaceof the substrate, wherein a transfer amount of pure water to therecording medium within a contact time of 100 ms is from 2 to 35 mL/m²and that within a contact time of 400 ms is from 3 to 40 mL/m², whenmeasured by a dynamic scanning absorptometer.
 29. The image formingmethod of claim 26, wherein the ink further comprises urethane resinparticles.
 30. The image forming method of claim 26, wherein the organicsolvent comprises a glycol ether compound.
 31. The image forming methodof claim 30, wherein the ink further comprises urethane resin particles,wherein a mass ratio of the glycol ether compound to the urethane resinparticles is in the range of from 0.4 to 1.8.
 32. The image formingmethod of claim 26, wherein the maximum value of logarithmic dampingratio of the ink film is from 0.01 to 1.30 and the time elapsed untilthe logarithmic damping ratio reaches the maximum value is from 100 to3,000 seconds, when measured by the rigid-body pendulum test at 60° C.33. An image forming apparatus comprising: a continuous sheet; a sheetfeeder configured to feed the continuous sheet; an ink comprising water,an organic solvent, and a colorant; a recording head configured todischarge the ink to the continuous sheet fed; a winder configured towind up the continuous sheet applied with the ink, wherein, when the inkis formed into an ink film, a maximum value of logarithmic damping ratioof the ink film is 1.50 or less and a time elapsed until the logarithmicdamping ratio reaches the maximum value is 3,800 seconds or less, whenmeasured by a rigid-body pendulum test at 60° C.
 34. The image formingapparatus of claim 33, wherein the ink further comprises urethane resinparticles.
 35. The image forming apparatus of claim 33, wherein theorganic solvent in the ink comprises a glycol ether compound.
 36. Theimage forming apparatus of claim 35, wherein the ink further comprisesurethane resin particles, wherein a mass ratio of the glycol ethercompound to the urethane resin particles is in the range of from 0.4 to1.8.
 37. The image forming apparatus of claim 33, wherein the maximumvalue of logarithmic damping ratio of the ink film is from 0.01 to 1.30and the time elapsed until the logarithmic damping ratio reaches themaximum value is from 100 to 3,000 seconds, when measured by therigid-body pendulum test at 60° C.